Front-end amplifiers used in equipment such as cable television sets and other broadband RF receivers require power supplied from a source that has very low distortion, i.e., a very low incidence of spurious signals. Additionally, in many applications such as cellular/PCS telephones, it is desirable that a single power supply be used.
In amplifiers using depletion-mode devices such as Field Effect Transistors (FETs), there is a need for a bias voltage to turn the devices OFF (non-conducting) from a normally ON (conducting) state. Such depletion-mode devices are commonly used in high-frequency devices constructed from materials in Groups III-V (e.g., GaAs). Common examples of high-frequency semiconductor devices built using these and other semiconductor materials are MESFETs, BJTs, and others.
If a depletion-mode device requires a negative bias supply, but the main circuit power supply is positive, then the negative bias potential must in some manner be generated from the positive potential. Conventional systems use a charge pump or an oscillator-rectifier supply to provide such a negative bias potential. But these conventional devices are generally bulky or difficult to integrate in a monolithic integrated circuit chip. Moreover, rectification generally produces spurious signals in such conventional devices.